One of our great contemporary writers has an unusual writing process. She spends a long time outlining a novel--I mean, a very long time--and then she writes the scenes out of order. I admire her work in every way, but I can't imitate her particular process. Another writer of my acquaintance creates synopses that run to eighty pages or more, so there are no surprises in the creation of the novel. Plenty of writers get by with three pages. My outlines run ten to twelve pages, and usually take me a week or so to do. I have to write in a linear fashion. It's my process, and I've learned to respect it, and to know that everyone's process is different.
What I have in common with all these authors, however, is the outline. Although it's far from being the most enjoyable part of writing a book, at least for me, it's a step I don't dare skip. Not only is the outline or synopsis an important marketing tool, since most of my contracts are based on synopses, it's immensely valuable as I write. I'm sure every one of the authors mentioned above feel the same way.
It takes discipline for me to stop writing--usually about fifty pages into a book--and turn to the work of the synopsis. It seems, at the early stage of a novel, a whole lot more fun to just write on and see where it all goes. Imagine, though, having four hundred pages under your belt and--no ending! Or a big, tangled plot problem with no way out! Hard as it is, I have to take the time to think objectively about plot, even though I'd rather be writing cool scenes and growing my characters, thinking up bizarre twists and turns.
An outline, or a synopsis, is essentially a present-tense narrative of what happens in the story. It touches on the main plot points, gives an idea of the structure and shape of the novel, and--most important of all--has an ending. It gives an editor an idea of what sort of book she's buying, and it's a reference for the writer to turn to when she's not sure what comes next.
Of course, a synopsis becomes an artifact once the book is written. Better ideas come up along the way, and new and improved endings present themselves. Still, if I have a synopsis I have a shape, and I have plot points. I have a structure, and a direction. I have some idea what the novel is really about. It's like weaving a tapestry, making sure all the threads not only tie together at the end, but form a satisfying pattern. Each part matters, and each part needs to fit into the overall design. There's nothing I hate more in a novel than random elements that don't pay off at the end.
I subscribe to Chekhov's dictum that the gun on the mantelpiece in Act One had better go off by Act Three. Outlines can ensure that satisfying climax.